Double-hung tilting sash type windows have become increasing popular. Much of this popularity is due to the tilting sash feature which allows both inside and outside surfaces of the window to be cleaned from the inside. A reoccurring problem with tilting sash type windows is how to achieve a tight seal between window frame and sashes without making it difficult to tilt the sashes. Additionally, the structural integrity of the window must be maintained at a sufficiently high level and unexpected motion of the sash must be reduced to promote safety. In the past, frames have been equipped with jamb liners having ridges, or ploughs, which extend into grooves in the side of the sashes.
One such configuration is shown in FIG. 2 of U.S. Pat. No. 4,799,333 to Westfall et al. In Westfall, these ploughs have outwardly disposed sides approximately perpendicular to the front face of the jamb liner. A similar arrangement is shown in FIG. 5 of U.S. Pat. No. 4,922,657 to Foss. The plough configuration of the jamb liner disclosed by Westfall et al. and Foss, however, do not project outwardly to engage with sashes having grooves with inward projections.
Tilting sash windows have also been equipped with locking slide blocks, such as the one disclosed in U.S. Pat. No. 4,610,108 to Marshik. Marshik discloses a double-hung window having a frame with a set of parallel jamb channels on opposite sides of the frame. Within each jamb channel is a slidably mounted locking block. A spring counterbalance mechanism is attached to a plate on each block. A pivot extends from proximate the lower end of opposite sides of each sash into locking cams housed within the block. The pivot allows the sash, which holds a window pane, to be rotated or tilted inward. As the pivot rotates, the cam forces serrated ends of a spring into opposite sides of the jamb channel to prevent the counterbalance spring from pulling up the blocks and sash while cleaning.
U.S. Pat. No. 4,813,180 to Scalzi discloses another locking sliding block for double-hung windows. Like the '108 patent, a locking block is slidably mounted within jamb channels and a pivot extends from opposite sides of the sash into a pivot button, or cam, in each locking block. Unlike the '108 patent, however, the pivot has a slot which engages a retaining ridge in the pivot button. This is intended to prevent dislocation of the pivots during transport and installation of the window due to deflection or bowing of the frame away from the sash. The locking block disclosed by Scalzi, although allowing the sash to pivot inside for easy cleaning of the window pane, does not allow the window to be conveniently removed from the inside.